Method and apparatus for detecting the presence of flame in the exhaust path of a gas turbine engine

ABSTRACT

A method and apparatus for monitoring the exhaust path of a gas turbine engine for the presence of unwanted flames downstream from the main combustion chamber(s). The system is comprised of an Electro-Optics Module containing sensors and associated processing electronics as well as collection and transmitting optics, which relay the radiant energy generated by a flame event to the sensors. The information generated by the sensors is directly related to the time based intensity of the flame event, which can suggest problems associated with the condition of combustion related engine components. This information can then be used by the engine owner/operator to assess the condition of the engine and determine the more efficient required maintenance schedule.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/388,604, filed Jun. 3, 2002, the contents of which are incorporatedin their entirety. The application claims benefit to PCT/US03/17040filed Jun. 3, 2003, which is incorporated herein by reference in itsentirety.

FIELD OF THE INVENTION

This invention relates to flame detection, and especially to a solidstate, fiber optic linked flame sensor that is particularly useful inconnection with sensing the flame in a gas turbine exhaust path as ameans of determining the condition of the fuel nozzle(s).

BACKGROUND OF THE INVENTION

The life cycle cost reduction for capital equipment such as gas turbinesis of great importance to end users such as the Navy, the shippingindustries and power generation stations to name a few. Regularmaintenance of gas turbine equipment by the operators is necessary tomaximize performance and fuel efficiency however the associatedincreased maintenance costs offset the benefits of shorter maintenanceintervals. Achieving the optimal maintenance plan, which minimizes thetotal operation and maintenance costs, depends on the availability ofaccurate performance degradation assessments from diagnostic andprognostic technologies.

These maintenance-timing decisions were historically founded on rigidschedules based upon hours of use or when the operator noticed a severedegradation in the performance or efficiency of the turbine. Themaintenance-timing was determined from examining the various turbinecomponents during normally scheduled maintenance or through mechanicalfailure and estimating whether the average turbine should be maintainedin a shorter or longer interval to maximize efficiency and minimizemaintenance costs. The shortfall of this method was that the maintenanceschedule was based on the average condition of a fleet of given turbinetypes, where unnecessary maintenance was done on some turbines whereneeded maintenance was forgone on other turbines resulting in poorperformance or worse, catastrophic failure and overall added costs. Insome turbines, when an injector or injectors were sufficiently clogged,the combustion process is uncontrolled and can cause visible flash offlame in the exhaust. This is hard to determine without specificdiagnostic equipment that has been historically a thermocouple. Theproblem is that once the degradation was significant enough for theoperator to perform out of schedule maintenance excessive fuel waswasted or worse was that fouling of the fuel nozzle caused harm to theturbine because of the shortfalls of the prior art diagnostic equipment.

Specifically, fuel nozzle fouling, can cause “hot starts” whereuncontrollable ignition results in flame propagation through the turbineand damage to hot section components which necessitates expensiverepairs and removing the affected turbine from service.

The Allison 501 turbine engine is used frequently in the Navy forshipboard power generation. The fuel nozzles in the Allison 501 engineoften become clogged with internal or external carbon deposits. Foulingtypically affects the pilot injection port more severely than the mainport. The pilot port is used during engine startup and idle when thefuel flow rate is too low for proper atomization by the main port. Apressure-driven flow divider directs the flow to the appropriate portfor proper atomization of the fuel for operation.

The fuel spray pattern is adversely affected by clogging and can lead toflame position problems that burn hot section components, and increasespotentially damaging “hot starts” or “no starts”. Clogged injectors candelay ignition (“light-off”) during engine start-up and cause a buildupof fuel in the combustor. When ignition finally occurs, the unusuallyrich fuel/air mixture can cause excessive gas temperatures, temperaturegradients and pressure gradients that damage hot section components. Theexcess fuel often produces a flash of flame in the engine's exhaust aswell that may be detected visually.

DESCRIPTION OF THE KNOWN PRIOR ART

Earlier flame detection systems which have been used to monitor variousgas turbine combustion processes include thermocouples, gaseousdischarge ultraviolet detectors, and, more recently, silicon carbide(SiC) ultraviolet detectors. Thermocouples have been used in thecombustion chamber area as well as in the exhaust gas stream. Theproblem of the thermocouple prior art in addition to having too slow ofa response time to adequately sense flame, thermocouples do not last forlong periods in the highly oxidizing atmosphere of a gas turbine.

Gaseous Discharge UV detectors have traditionally been used to validatethe proper ignition of the combustion flame. They are extremely fastdevices with a wide operating temperature range. When properlyconstructed they are non-responsive to the radiant energy of hotsurfaces in the combustion chamber. Their drawbacks are in many waysrelated only to industry perception. More specifically, they areconsidered by most to be antiquated technology. Additionally they sufferfrom requiring supply voltages in excess of 325 volts DC. Siliconcarbide UV sensors are considered by most to be the modern replacementfor the Gaseous Discharge UV detectors.

Turbine manufacturers and users are not presently known to be making useof any optical means to alert them to the presence of a flame in theexhaust section of their engines. Rather, they are utilizingthermocouple arrays to profile the temperatures in various locationsthroughout the exhaust path stream. The time durations of the flameevents observed during our testing were so short (in the realm of asecond or less), that thermocouple technology would not be responsiveenough to accurately detect them. Therefore the improvement in reducingunnecessary maintenance costs is minimal and not cost effective using athermocouple because of the shortfalls consistent with that method ofmonitoring flame in the exhaust section of the turbine.

OBJECTS OF THE INVENTION

Accordingly, it is an object of the instant invention to provide amethod of determining the condition of the nozzle fouling to maximizefuel efficiency.

It is an object of the present invention to detect the presence of aflame, as it exists in the exhaust path of a gas turbine engine.

It is a further objective to be able to delineate differences in theintensity and duration of flame presence in the exhaust stream of a gasturbine engine.

It is yet another objective to be able to assign a measure of nozzlefouling (coking) certainty as a result of the analysis of the signalgenerated by the electronics of the optical monitoring equipment.

It is a continued object of this invention to serve in a feed back roleto a centralized control system acting in the capacity of a ConditionedBased Monitor, for equipment operation maintenance.

SUMMARY OF THE INVENTION

The present invention achieves the above-described objectives byproviding an Electro-Optics Module (EOM), Fiber Optic Cable Assembly andan Optical Viewing Port or alternatively a sensor directly mounted thatproduces a signal in the presence of a flame directly attached to theexhaust port. The EOM houses the sensor(s) and signal processingelectronics. The Optical View Port mounts to the gas turbine enginepreferably down stream from the combustion chamber(s) and collects theradiant energy from the flame and focuses it on the tip of the FiberOptic Cable Assembly. The Fiber Optic Cable Assembly transmits theradiant energy collected by the Optical View Port to the sensor(s)located inside the EOM.

The sensor(s) may optionally be assembled in modules containing optionalcustom discrete optical filters and amplification circuitry. The opticalfilters guarantee that the spectral energy reaching the sensor elementsis restricted to wavelengths specific to the signatures of the flamesource, however any sensors respondent to unfiltered energy within thevisible light spectrum would satisfy the inventions requirements.

The sensor analog signals, which are proportional to the intensity ofthe radiant energy received, are optionally recorded either on aphysical chart or indicator, or preferably converted to digital signalsand fed into the EOM's microprocessor where they are compared using theMeggitt developed algorithms. The result of the processed signal is adetermination of flame signal intensity and its duration. These time anddate stamped signal traits are stored within the EOM's self-containedmemory for later evaluation. Additionally these signals are available tobe fed to the Condition Based Monitoring data collection center for theengine.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a plan view of a fiber optic linked flame sensor.

FIG. 2 is a partial side view of an optical probe.

FIG. 3 is a partial cut-away view of a fiber optic cable.

FIG. 4 is a partial cut away view of an individual fiber.

FIG. 5 is a view in a schematic form of an electro-optics module.

FIG. 6 is a theoretical plot of the relative spectral signature of aburning hydrocarbon fuel together with specific emission bands andvarious sensor detection regions.

FIG. 7 is a plot of the typical spectral response of an OSRAM BPW 21Silicon Photodiode.

FIG. 8 is a plot showing the spectral irradiance differences between abench-top propane Bunsen burner source and a 1900° K. graybody in theultraviolet region.

FIG. 9 is a pictorial representation of a flash event analysis asperformed by the detection algorithm.

FIG. 10 is a table with test fuel nozzles and their known performancecharacteristics.

FIG. 11 is a table showing resulting flame presence in the exhaustsection of a gas turbine in relation to the condition of the fuelnozzle.

FIG. 12 is a reading (raw signal) of spectral energy observed in theexhaust section of a gas turbine with a clogged nozzle.

FIG. 13 is a schematic diagram illustrating an example of aspectrometer.

FIG. 14A and FIG. 14B are graphs showing results of test run 6.

FIG. 15 is a graph showing results of test run 7.

FIG. 16A and FIG. 16B are graphs showing results of test run 8.

FIG. 17 is a graph showing results of test run 9.

FIG. 18A and FIG. 18B are graphs showing results of test run 10.

FIG. 19A and FIG. 19B are graphs showing results of test run 11.

FIG. 20A and FIG. 20B are graphs showing results of test run 1.

FIG. 21A and FIG. 21B are graphs showing results of test run 2.

FIG. 22A and FIG. 22B are graphs showing results of test run 3.

FIG. 23A and FIG. 23B are graphs showing results of test run 4A.

FIG. 24A and FIG. 24B are graphs showing results of test run 4B.

FIG. 25A and FIG. 25B are graphs showing results of test run 5.

FIG. 26 is a graph showing results of test run 6.

DETAILED DESCRIPTION

In reference to FIGS. 1–5, according to one potential embodiment of thepresent invention is at least one fiber optic flame sensor 10 formonitoring the presence and/or intensity of the flame in the exhaustsection of a gas turbine engine generally consists of three componentsections; a high temperature probe or optical viewing port 20, at leastone fiber optic cable 30, and an Electro-Optics Module 40 (E.O.M.). Asdescribed in detail below, the high temperature probe/optical viewingport 20, mounts directly on the engine in a location, which will providean adequate view into the exhaust portion of the turbine thus acting asa sight pipe. The fiber optic cable 30 transfers the radiantelectromagnetic energy emitted by an uncontrolled combustion flame fromthe viewing port 20 to the E.O.M. 40. The E.O.M. 40 preferably containssolid-state electronics for converting a selected wavelength region ofthe radiant electromagnetic energy to an electrical signal that ismonitored, in a known manner, to determine the presence or absence ofthe undesirable flame in the exhaust plenum. The electrical signal thusindicates the presence of a flame, or absence of flame depending on thesetup of the equipment. Furthermore, the monitoring can include thegathering of additional information about the flame condition such asintensity and duration of the event. In FIG. 8 it displays thedifference between a bench-top propane Bunsen burner flame 56 and a1900° K. greybody 58. The difference is clearly discernable to anaccurate sensor calibrated to a flame radiation source.

The E.O.M. 40 could optionally use an analog method such as a simplevisual indicator such as an indicator light or a paper chart that wouldserve as a record of the event of flash in the exhaust that has a veryshort duration. Or the signal can be converted to a digital signal forfurther processing by a digital computer. An example of an optical viewport and fiber optic linked cable assembly suitable for use are furtherdescribed in U.S. Pat. No. 5,828,797 entitled “Fiber Optic Linked FlameSensor”, the contents of which are herein incorporated by reference intheir entirety. Several concepts related to the monitoring of a flameare disclosed in U.S. Pat. No. 6,071,114 entitled “Method and ApparatusFor Characterizing a Combustion Flame”, which is also incorporated byreference in its entirety.

Turning now to FIG. 2, the optical viewing port 20 is constructed ofhigh temperature materials that can withstand the intense temperaturesassociated with the exhaust gasses. Preferably, the end portion 25 ofthe port 20, which mounts to the exhaust section may be constructed ofeither 316L stainless steel or Hastelloy X due to its corrosionresistant nature at elevated temperatures and in marine environments.The end portion 25 of port 20 mounts to the exhaust of the turbinepreferably using threads 27, that are ¾ NPT mounting threads. Threads 27can be replaced with welding, riveting, quick disconnect or variousother methods of fastening known in the art. It is preferable that thefitting be standardized and provide a good seal to avoid escape ofturbine exhaust gasses. A thread fit is therefore preferable because itis inexpensive and effective at tightly connecting and sealing the probeto the exhaust while allowing for ease of removal.

Additionally, other materials with similar minimum performancecharacteristics can be utilized in other possible probe configurationsand material combinations to provide the needed site pipe into theexhaust chamber of probe/port 20.

In particular, it is important that whatever material is used in theconstruction of the optical view port probe, it must not impart unduestrain to the Kovar ring 29 containing the brazed sapphire window 28.The port 20 acts as a sight pipe into the exhaust section and maycontain a braze-sealed sapphire lens 28. The instant invention onlyrequires that the port 20 act as a minimum as a sight pipe and thereforeit is anticipated that many substitutes may be fashioned as long as ithas the capacity to withstand the heat of the turbine exhaust andsimultaneously transmit the spectral radiation from the flame in theexhaust path to the E.O.M. 40, or it can be replaced with a sensorassembly capable of directly monitoring the presence of flame. The endportion 25 of port 20 mounts to the gas turbine's exterior exhausthousing, preferably positioned as close to the beginning of the exhaustsection as feasible ensuring that the Radiant energy is transferred fromany flame present in the exhaust into the sight tube bore 24 of theprobe 20 through opening 23, and then to the fiber optic cable interface26 into the fiber optic cable 30. The Radiant energy is potentially, butnot limited to all light/energy produced within the spectral range of200 nm to 800 nm, but preferably it is the frequency associated with thepresence of a flame; this would obviously include all theelectromagnetic frequencies in the infrared associated with the byproducts of hydrocarbon combustion such as H₂O and CO₂.

In one embodiment, the probe 20 has an overall length of about 2.2∀, andthe sight tube opening 24 containing ¾-14 NPT threads and a lensaperture of approximately 0.48∀, these dimensions are not critical andcan be changed based on matching the physical parameters of the leastexpensive components produced at the time of manufacture and thephysical requirements as they relate to efficient access to the exhauststream.

The probe 20 dimensions are not critical as long as it functions toefficiently couple the radiant energy from exhaust of the gas turbine tothe optical cable 30. The optical cable 30 can potentially be eliminatedif the E.O.M. 40 is sufficiently dimensioned to fit directly upon probe20 and heat resistant enough to survive close proximity to the exhaustenvironment of the gas turbine or a flame sensor 10 (direct mounting ofthe flame sensor to exhaust not displayed) is of sufficient constructionand cost effective to be directly mounted to the exhaust portion of theturbine.

The sapphire lens 28 is braze-sealed to a Kovar ring 29, which then isthen welded 21 into the probe body 20. The sapphire lens seal ispreferred because it is capable of withstanding gas temperatures of 900degree F. at pressures reaching 500 psi, but other materials can besubstituted having suitable characteristics for the monitoringenvironment. This lens 28, therefore, acts as the protective barrierseparating the combustion process from the other optical systemcomponents. The sapphire lens 28, Plano convex in the preferredconfiguration, focuses the radiant emission energy resultant from thecombustion process into the suitable acceptance angle matching thenumerical aperture of the fiber optic cable 30, the tip of which isinserted into cable interface 26. The interior walls of Kovar ring 29 ofthe brazed lens assembly welded within the sight probe are optionallyplated with gold or other suitable materials to help prevent oxidativecontaminants from fouling the optical surfaces.

The fiber optic cable 30 transfers the radiant energy projected throughthe high temperature probe lens 28, from the errant flame potentiallypresent in the exhaust stream to the (E.O.M.) Electro-Optics Module 40.

Referring to FIG. 3, the fiber optic cable 30 contains at least oneoptical fiber 33 and may be composed of a plurality of individual fusedsilica optical fibers 33, and is preferably as short as possible inlength to minimize losses but distances of about twenty feet or more inlength are possible. Other materials that provide the necessary lighttransmissibility such as polymers may be substituted if they are capableof long-term use in the environment of the turbine.

As shown in FIG. 4, in one embodiment an optical fiber 33 has a core 34that has a low transmission loss, typically used is a pure fused silicathat is preferably 200 micrometers (microns) in diameter or othermaterials such as polymers that offer sufficient transmission of energyover the desired cable length.

Optionally, if required for sufficient energy transmission for longerselected cables, over the core 34 is a cladding 35 composed of dopedfused silica 10 microns thick. A buffer layer 36 of either polyimide orgold covers the cladding 35 in a thickness of about 5–15 microns,preferably 10 microns. In the first few inches, preferably about six totwelve inches, of the fiber optic cable at the high temperature probeend 37 (FIG. 1) of the cable; a gold buffer layer 36 rated at 900 degreeF. is used. The remainder of the cable is provided with a polyimidebuffer 36, rated at 540 degree F.

A more cost effective cable construction can be designed that eliminatessome or all of the above described features. The cable is limited in itsdesign only in that it must provide sufficient transmission of radiantenergy to the sensor(s) and capable of withstanding the environment inwhich it is routed either in a high or preferably that of low heatenvironment to reduce expenses. It would be an obvious modification toone skilled in the art to design more or less features into the cable tosave expense or to design for a less heat intensive environment.

As shown in FIG. 3, one potential configuration of the group of aplurality of fibers 33 is closely packed in a hexagonal arrangement andsheathed in fiber glass cloth 38 and a stainless steel braid 39. Theends of the cable 37 that are terminated in stainless steel ferrules 31(FIG. 1) of a proper shape and size to interface with the hightemperature probe 20 on one end, and the E.O.M. 40 on the other end. Theminimum amount of fibers needed to transfer the radiant energy to thesensor is one, but additional fibers may be added for use withadditional sensors or for redundancy purposes.

Turning to FIG. 5, the Electro Optics Module 40 (E.O.M.) is preferablylocated at the so-called low temperature end of the fiber optic cable37. The ambient temperature where the E.O.M. is located is preferably nogreater than 125 degree C., thus permitting conventional, low costelectronics to be used in the E.O.M. 40. The function of the E.O.M. 40is to convert the radiant energy transmitted from a flame through thefiber optic cable 30 into an electrical output signal. To accomplishthis, the tip 41 of the low temperature end 37 of the fiber optic cable30 directs electromagnetic radiation with the aid of focusing optics 43onto the active area of a solid state sensor 44 mounted optionally on acircuit board 45. Input and output to the circuit board is providedthrough a port 46 on the E.O.M. 40. The port 46 is preferably connectedto a recordation device 48. On the occurrence of a flame-condition inthe exhaust path, the radiant energy at the sensor 44 causes the E.O.M.40 to provide an electrical signal, in a known manner, to the memorystorage apparatus 48, either digital or analog indicating potentialnozzle fouling to the operator or control electronics of the turbine.

One potential choice for solid-state sensor 44 is a Silicon Photodiodethat is sensitive to the presence of a flame, which is usually filteredto monitor only the spectral range of a flame. This detector (BPW 21) isproduced by OSRAM Opto Semiconductors that are available in TO-5transistor cans. Other types of sensors may be substituted provided thatthey respond to at least a portion of the radiant energy produced fromthe flame in the wavelength range of 200 nm to 900 nm. The sensor 44 maybe part of an optional transimpedance amplifier circuit 47 thatgenerates a voltage output signal proportional to the intensity level ofthe radiation received within a specific spectral bandwidth. In additionto containing the sensor 44 and amplification electronics 47, the E.O.M.also may optionally contain processing electronics 49, depending on auser's requirements.

In FIG. 6 a chart displays a spectrum of 200 to 750 nm and the relativespectral signature of a burning hydrocarbon and various sensor detectionregions. Alternative detectors that can be selected are constructedusing wavelength selecting sensing elements such as SiC (200–375 nm),GaN (200–365 nm), AlGaN (200–320 nm), and a relatively new UV photodiodehaving a spectral response range from 215 to 387 nm. This UV photodiodeis based on semiconductor technology whereby a thin film deposition viathe sol-gel process on the semiconductor determines its spectralproperties. All of these detector types are available through BostonElectronics Corporation, Brookline Mass.

Although hydrocarbon flames are know to have a significant emission peakat 310 nm, the data acquired during testing would seem to indicate thatthere may not be enough radiant energy present in the exhaust path flameto excite these types of detectors without additional components toincrease signal intensity. It is not to say that if mounted in adifferent location on the engine, however, that they would not worksufficiently well.

In an alternative method using these types of detectors, the selectivespectral response could be considered advantageous. This would be thecase in an application where the exhaust plenum may have many openingswhere ambient visible light may result in a false flame event. Theseevents could occur if the viewing probe were to collect the energyproduced by reflected sunlight or high intensity inspection lightingequipment. During the testing associated with this instant invention,there were no adverse effects realized with the ambient lighting presentin the turbine package. More specifics as they relate to flame sensingwith detectors such as those similar in nature to SiC UV detectors canbe found in U.S. Pat. No. 5,828,797 and is incorporated in its entirety.

Alternative detectors having a spectral response from 200 nanometers(nm) to approximately 375 nm include, Gallium Nitride (GaN) UV detectoravailable from APA Optics, Inc., Minneapolis, Minn., andSilicon-on-Insulator technology based UV photodiodes available fromSpire Corporation, Bedford, Mass.

In one embodiment the sensor 44 is a SiC UV photodiode detector that hasa UV spectral response that is suitable for detecting the presence of aflame in the exhaust path. Referring to FIG. 6, a dramatic spike 50 isshown in a plot of the radiant emission energy from a burninghydrocarbon fuel the spectral radiant intensity of the emission iscentered at 310 nm. FIG. 7 displays, the spectral response 51 for aBPW21 Silicon Photodiode useful for detecting the emission of the flameof a burning hydrocarbon with its most effective range being about 300to 800 nm.

Currently only a few different types of sensors are utilized to monitorthe energy output of flame mostly because of cost associated withchoosing other less common sensors. This list represents a few ofpossible wavelengths that one may possibly wish to monitor to determinethe presence of flames as alternatives to the current sensors currentlyutilized.

Emission Flame Element Species Relative Relative Species Center(compound Emission Electronic Comments wavelength Wavelength or StrengthElement Emission about (nm) (nm) molecule) 1 to 7 I.D. Strengthemissions 234.8 Be 950 234.9 As 350 249.7 B 1000 255 P 950 265.9 Pt 2000282 Hf 1200 287.8 Sb 1000 288.2 Si 1000 303.9 Ge 750 306.4 OH— 6 306.8Bi 9000 312.2 OH— 6 314.4 CH 7 315.66 CH 6 318.5 OH— 2 322.1 Ir 5100325.4 OH— 1 326.5 Cu 10000 331.1 Ta 1100 336 NH 2 358.4 CN 3 358.6 CN 3358.7 C2 3 359 CN 2 379.8 Mo 29000 386.2 CN 1 387.1 CN 6 388.3 CN 6387.2 CH 6 396.1 Al 9000 403.3 Mn 27000 405.8 Pb 95000 407.9 Nb 12000413.8 Ce 2700 417.2 Ga 10 422.7 Ca 50 426.5 Cr 20000 426.7 C 1000 431.2CH 7 432 W 2200 432.4 CH 7 435.8 (253.6) Hg 4000 (15000) 436.5 C2 7437.1 C2 7 437.9 V 12000 438.3 C2 7 439.7 Fe 3000   442 (352.4) Ni 110(8200) 451.1 In 18000 452.5 Sn 40 455.4 Ba 65000   458 (460.3) Cs 100000466.9 C2 7 467 Sr 65000 467.9 C2 7 468.5 C2 7 469.8 C2 7 471.5 C2 7473.7 C2 7 477 C2 2 477.2 Zr 870 481.4 (345)   Co  100 (21000) 498.7 Ti5800 499.7 C2 7 509.8 C2 7 512.9 C2 7 516.5 C2 7   518 (285.2) Mg 400(6000) 535 Tl 18000 546 (328) Ag 1000 (55000) 547 C2 5 550.2 C2 6 554.1C2 6 558.6 C2 6 563.6 C2 6 589.5 Na 80000 590 C2 2 592.3 C2 2 595.9 C2 5600.49 C2 5 605.9 C2 5 612.2 C2 5 619.1 C2 5 627.8 Au 600 636.2 Zn 1000643.9 Cd 2000 653.4 C2 1 659.9 C2 2 667.7 C2 2 676.3 C2 2 678 (671) Li3600 685.9 C2 2 722.7 H2O 6 746 OH— 6 766.5 K 25 771.5 C2 6 780 Rb 90000785 OH— 6 790.8 C2 6 795.7 H2O 6 810.8 C2 6 822.7 H2O 6 827.8 OH— 6875.1 C2 6 898.1 C2 6

Infrared

Original Wavelength Band Head (microns) Center 1.8752 H2O v. strong2.3467 2.2929 CO ″ vib-rotation overtone 3.3762 2.3221 CO ″ 2.40642.3519 CO ″ 2.6618 H2O v. strong 2.6912 CO2 strong 2.7337 H2O strong2.7672 CO2 strong 2.8007 OH— weak masked by CO2 and H2O 3.1722 H2Ostrong 4.2557 4.1713 CO2 v. strong modified by self absorption 4.2791.1912 CO2 4.2955 4.211 CO2 4.297 4.2057 CO2 4.3014 4.214 CO2 4.6644 COmoderate self absorabed and masked by CO2 4.7228 CO ″ 4.7825 CO ″ 6.2698H2O v. strong 13.8699 CO2 moderate intensity about 1/200th of 4.3 micronintensity 14.9794 CO2 ″

There is thus provided a fiber optic linked flame sensor which providesrapid, reliable, and cost effective optical monitoring of the presenceof flame within the exhaust chamber of a gas turbine engine to providereduced maintenance costs through the accurate diagnosis of the presenceof a clogged fuel nozzle without teardown of the turbine.

As discussed previously the spectral energy indicating the presence offlame in the exhaust of a turbine can encompass the entire visiblespectrum and wavelengths of 200 to 1000 nm. The wavelength monitoredwith sensors can ideally range from 200 nanometers (nm) to 800 nm. TheCH emission band head at 431 nm, monitoring from 350 to 500 nm, and theOH emission band head at 310 nm monitoring from 250 nm to 400 nm havebeen found to be effective in practice. Additional spectral data fromthe current broadband region of about 550 nm to 650 nm, and thebroadband region of 400 nm to 500 nm are also effective in flamedetection given the absence of background radiation sources withsufficient energy to excite these sensors.

Further sensor detection of flame can be accomplished in the infraredregions. The regions of 2.9 and 4.4 micrometers that have beenassociated with flame detection and therefore sensors capable of fastresponse time in the region of approximately 1.0 to 5.0 micrometers canalso satisfy the flame detection requirements. The sensor utilizedshould be capable of responding in less than approximately 100microseconds (μs), but may still be effective between 100 and 300microseconds to effectively monitor the presence of flame in the exhaustdepending on its duration within the spectrum discussed above. Adetection system based solely on infrared technology would require fiberoptic core materials other than fused silica. One option would be to usesapphire, however at this time this option would be extremely expensiveand a less cost effective solution.

In another embodiment remote monitoring of the flame event using a fastscanning miniature spectrometer is performed. FIG. 13 is a schematicdiagram illustrating an example of a spectrometer 100. This embodimentuses fiber optics to locate the spectrometer 100 to an environment,which is conducive to its operating limits. The basic principle ofoperation would be as follows: Light gathered by the view port attachedto the exhaust plenum and transmitted by the fiber optic cable to afiber optic connection 102, enters the spectrometer 100 through a fixedaperture 103 and optical filter 104. The light energy then strikes acollimating mirror 105 and is directed at the diffraction grating 106.The light is refracted by the grating 106 and directed toward a focusingmirror 107. The diffracted light strikes the focusing mirror 107 whereit is reflected and focused onto a detector array 109. In front of thedetector array 109 is a lens 108, which concentrates light onto theindividual detectors 109. There is also an order sorting filter 110known in the art to limit the effect of second and third orderwavelength harmonics. Finally, each detector element (pixel) responds tothe individual wavelength of light that strikes it. The signals are thenfed into a microprocessor, which interprets the various signal strengthsand produces information relative to the intensity of the individualwavelengths of light as received by the detector array. This informationcan then be used to determine the spectral nature of the flame conditionbeing monitored. This sensor technology as produced by Ocean OpticsInc., Dunedin, Fla.

This can be configured and customized to meet the needs of theapplication, i.e., usable spectral range. The total spectral capabilityof such a system can be realized from 200 nm up to 1600 nm. However, toscan the entire range would require more than one spectrometer beingsupplied the same energy from the flame. The optical signal could besplit and fed to however many spectrometers are required in order toaccurately assess the spectral nature of the flame.

The basic configuration of such a system as produced by StellarNet Inc,Oldsmar, Fla., is describe below. StellarNet's miniature fiber opticspectrometers, industrial process probes, optical fibers, light sourceaccessories and SpectraWiz® software are process control and qualitycontrol monitor workhorses for analytical instrumentation designed tomeasure light wavelength absorbance, transmission, reflection, color,emission, irradiance, and fluorescence. Measurements for ranges in theultraviolet (UV 190–400 nm), Visible color (VIS 350–850 nm), short-waveNear Infrared (NIR 500–1200 nm), and Near Infrared (XNIR 1200–1600 nm)are easily performed by portable EPP2000™ (parallel port interface) orISA2000™ (PC plug-in card) fiber optic spectrometers.

CCD or Photo Diode Array spectrograph optics have no moving parts ordetector sockets and could be utilized in flame detection. The units aredesigned to be vibration tolerant and use thermal stabilization suitablefor process applications. The EPP2000C™ spectrometer has no mirrors. Ituses an aberration corrected holographic, concave diffraction gratingfor superb imaging while minimizing stray light. This instrument coversthe UV and VIS ranges in one unit (190–850 nm).

There is also similar technology developed, which will provide the sametype of information from 1.0 micrometers (μm) to 5.0 μm. This equipmentis available through Spectraline Inc., West Lafayette, Ind. There hasalready been work done and published in the area of flame research usingthis type of equipment. NASA Tech Briefs, published in November 2000authored by Yudaya Sivathanu and Rony Joseph of En'Urga Inc. for GlennResearch Center.

A spectrometer has been developed for acquiring transient emission andabsorption spectra in the wavelength range from 1.2 to 5.0 μm and couldbe used to characterize flames, turbulence, and other transientphenomena that interact with infrared radiation. In one potentialembodiment an infrared spectrometer measures the spectrum at arepetition frequency of 390 Hz. The spectrometer optics include achopper, two prisms that serve as dispersers, and parabolicoptical-path-folding mirrors. The spectrally dispersed light isprojected onto a 160-pixel linear array of lead selenide photodetectors.The spectrometer also includes electronic circuitry for controlling thechopper, synchronizing readout from the pixels with the chopping cycle,and sending data to an external computer or data logger.

A method of determining presence of flame or fuel nozzle condition ofthe present invention comprises the steps of: providing anElectro-Optics Module (EOM) 40, Fiber Optic Cable Assembly 30 and anOptical Viewing Port 20; monitoring the operation of the turbine with asight pipe prior to the commencement of operation of the turbine;operating the gas turbine; transferring radiant energy from the turbineexhaust section via a fiber optic cable 30; determining with the EOM 40that a condition of flash exists; indicating to the operator thepresence of flash in the turbine exhaust.

A method of detecting the presence of flame in the exhaust furthercomprises the steps of providing sensor(s) and optional signalprocessing electronics. The Optical View Port 20 mounts to the gasturbine engine and collects the radiant energy from the flame andfocuses it on the tip of the Fiber Optic Cable Assembly 30. The FiberOptic Cable Assembly 30 transmits the radiant energy collected by theOptical View Port to the sensor(s) located inside the EOM 40.

The sensor(s) are assembled in modules optionally containing customdiscrete optical filters and amplification circuitry. The opticalfilters guarantee that the spectral energy reaching the sensor elementsis restricted to wavelengths specific to the signatures of the flamesource.

The method of detecting the presence of flame in the exhaust furthercomprises the steps of converting an analog signal to a digital signal;comparing signals via an algorithm; storing processed signal with a timedate stamp within a memory. The sensor analog signals, which areproportional to the intensity of the radiant energy received, areconverted to digital signals and fed into the EOM's microprocessor wherethey are compared using the Meggitt developed algorithms. The result ofthe processed signal is a determination of flame signal intensity andits duration. These time and date stamped signal traits are storedwithin the EOM's self-contained memory for later evaluation.Additionally these signals are available to be fed to the ConditionBased Monitoring data collection center for the engine.

One embodiment uses a fiber optic linked flame sensor for continuousoptical monitoring of the exhaust of a gas turbine engine. The systemincludes a high temperature optical probe 20, a fiber optic cable 30,and electro-optics module 40. The high temperature probe is mounted onthe engine skin and sighted in a manner so as to view the exhaust gasfor presence of flame that indicates fouling of the fuel nozzle orotherwise a condition of uncontrolled combustion. The appropriatelyconstructed fiber optic cable connects the high temperature probe withthe electro-optics module. The radiation transmitted via the fiber opticcable is then received by a photodiode located in the electro-opticsmodule and coupled with appropriate electronics.

Test Results-Allison-501 Turbine

The Allison-501 turbine consists of six nozzles arranged in a circularpattern with a number assigned to the nozzle corresponds to the positionon the turbine, when viewed from the compressor end and numbered in acounterclockwise fashion. The invention disclosed herein is tested on anAllison 501 turbine but it is applicable to all other known turbines andconfigurations. One skilled in the art would be able to adapt thispreliminary testing information to monitor any other turbine's operatingcondition and nozzle condition to prevent damage to the hot section of aturbine from clogged or dirty fuel nozzles. In FIG. 10 the conditions ofthe nozzles are examined. In FIG. 11 the severity of flash is related tothe condition of the nozzles of the turbine. In FIG. 12 the raw data ofa test run is displayed.

The table below represents data collection from a series of testsinvolving one embodiment of the instant invention. The data collectionwas manually initiated approximately 5 to 10 seconds before the gasturbine was started. All runs that displayed flash in the exhaust weredisplayed in greater detail for the portion of the period of flash.

Optical Evidence Sensor Flash Nozzle Condition (Severity Ranking)* OfVisual Detection Duration Date Test Run Nozzle 1 Nozzle 2 Nozzle 3Nozzle 4 Nozzle 5 Nozzle 6 Flash (Yes/No) (ms) 12-Jun 1 Clean CleanClean Clean Clean Clean No Not Taken n/a 2 Clean Clean Clean Clean CleanClean No Not Taken n/a 3 Clean Clean Clean Clean Clean Clean No NotTaken n/a 4 Clean Clean 1 Clean Clean 2 Small Flash Not Taken n/a 5Clean Clean 1 Clean Clean 2 No Data Lost n/a 6 Clean 4 1 Clean 3 2 NoYes 50–80 7 Clean 4 1 Clean 3 2 No No n/a 8 Clean 3 5 Clean 4 2 SmallFlash Yes 22 9 Clean 3 5 Clean 4 2 Small Flash No n/a 10 Clean 3 5 Clean4 6 Large Flash Yes 930  11 Clean 3 5 Clean 4 6 Small Flash Yes 330 13-Jun 1 Clean 3 5 Clean 4 6 Large Flame Yes 800  2 Clean 3 5 Clean 4 62 Flashes Yes 470  3 Clean 3 5 Clean 4 2 Medium Flash Yes 40 4A Clean 41 Clean 3 2 No Yes 33 4B Clean 4 1 Clean 3 2 Medium Flash Yes 38 5 CleanClean 1 Clean Clean 2 Minimum Flash ?Yes? 30 6 Clean Clean 1 Clean Clean2 No Yes n/a Ranking # 1 - Least severe nozzle fouling Ranking # 6 -Most severe nozzle fouling

The table displays the information obtained from the test and the knowncondition of the nozzle immediately prior to the onset of testingconfirmed through a visual inspection of each nozzle. The instantinvention was shown to provide the time duration and relative intensityof the flash event. The data shown above shows a high correlationbetween the condition of the nozzle(s) and presence of flame in theexhaust and provide a strong predictive tool useful in determining amaintenance schedule for each independent gas turbine to maximizeperformance and eliminate unexpected downtime.

Exhaust flash was detected in test run 6 as shown by FIG. 14A and FIG.14B with nozzle 2 and nozzle 5 displaying moderate to severe fouling outof the six nozzles present during turbine startup displayed at around 9seconds into measurement circled on the graph of FIG. 14A. The flashevent was displayed in greater detail showing the response of theinstant invention to the short duration of the presence of flame in theinitial stages of fouling of the turbines six fuel nozzles with theflash clearly showing an impulse response above the average intensity ofthe background radiation without the presence of flash in the exhaust.

Subsequent test run 7 having similar nozzle condition failed to show anyflash present with similar conditions, as shown by FIG. 15.

Test run 8 having nozzle 3 and 5 showing severe clogging and nozzles 2and 6 showing partial clogging displayed a flash event of greaterintensity, as shown by FIG. 16A and FIG. 16B. The intensity of the flashbeing relatively proportional to the overall condition of the state ofthe nozzles of the turbine.

Test run 9 having similar nozzle condition to that of test 8 failed toregister a flash event even though evidence of visual flash was recordedduring testing, as shown by FIG. 17. Individuals conducting the testsvisually determined the presence of flash. There was some confusion asto whether Test run 9 ever truly produced a visible flash.

Test run 10 4 of the 6 fuel nozzles moderately to severely fouledproducing both a high intensity flash with a long duration, as shown byFIG. 18A and FIG. 18B.

Test run 11 having similar nozzle condition to that of test run 10 has 4of the 6 fuel nozzles moderately to severely fouled producing both a lowintensity flash with a relatively long duration, as shown by FIG. 19Aand FIG. 19B.

Test run 1, as shown by FIG. 20A and FIG. 20B, conducted on the next dayof testing had the same nozzle condition to that of previous test run 11having 4 of the 6 fuel nozzles moderately to severely fouled producingboth a low intensity flash with a long duration.

Test run 2, as shown by FIG. 21A and FIG. 21B, conducted on the secondday of testing had the same nozzle conditions to that of previous testrun 1 having 4 of the 6 fuel nozzles moderately to severely fouledproducing both a low intensity flash with a long duration.

Test run 3, as shown by FIG. 22A and FIG. 22B, conducted on the secondday of testing had similar nozzle condition to that of previous test run2 having 3 of the 6 fuel nozzles moderately to severely fouled producingboth a high intensity flash with a short duration.

Test run 4A, as shown by FIG. 23A and FIG. 23B, conducted on the secondday of testing had 2 of the 6 fuel nozzles moderately fouled producingboth a low intensity flash with a short duration that was detected bythe optical sensor but not visually.

Test run 4B, as shown by FIG. 24A and FIG. 24B, having nearly identicalconditions to run 4A displayed a high intensity flash with a shortduration.

Test run 5 displayed, as shown in FIG. 25A and FIG. 25B, having 4 of the6 nozzles clean, with 2 partially fouled produced a low intensity flashof short duration.

Test run 6, as shown in FIG. 26, had identical nozzle condition to test5 and no flash was detected. The test data above is not intended to bethe only potential embodiment and is only an initial test using oneembodiment.

The testing data obtained from the Allison 501 turbine shows thecorrelation between the presence and duration of flame in the exhaust ofa turbine and the condition of the nozzles. Therefore analyzing theabove preliminary data findings it is clear that with a single testingevent of the startup of the gas turbine if the sensors detect a flame ofhigh intensity (compared to the background radiation intensity) and/or aduration of a flame signature lasting for a period of at least 30 ms induration it should indicate to the operator of the turbine that themajority of the nozzles may be partially fouled and that it is anindicator that maintenance should be performed preferably before damageto the turbine occurs. The results displayed in test runs 6, 8 and 10–11on the first test date and test runs 1–4B on the second test asdisplayed in the table above are preliminary findings and would need tobe correlated to costs to perform maintenance verses the probability ofdamage to the hot section of the turbine to determine if immediatemaintenance of the turbine was necessary. This exact information when tocease operations to prevent permanent damage could be ascertained withmore certainty after longer term evaluation of test data over a periodof months or even years of a fleet of turbines with proper flamepresence monitoring. This long-term maintenance evaluation would not bepossible without the data acquired from the flame sensor(s).

The testing for normal service should ideally be performed from thefirst start of the turbine after entry into service when the fuelnozzles are known to be in a clean condition. This initial data can beset as a baseline for storage in the E.O.M. to indicate the idealcondition of the turbine. Subsequent data from continued operation ofthe turbine can then be compared to the initial baseline to produce atrend line to indicate to the operator the anticipated time for servicefor the individual turbine assuming a linear progression of clogging andif an unexpected change in the condition of the fuel nozzle occurs asdiscussed above an alarm or indication to the operator that immediateservice is needed to prevent damage to the hot sections of the turbine.

The following is an explanation for the graph of FIG. 9, which describesthe methodology for determining the nature of a flash event: Thethreshold reference level 60 is a smoothing function of the sampleintensity 62. It will be used to establish the trip point 64 forstarting to integrate the flash interval 76. Once the relative intensity66 reaches the trip point level 68, the reference threshold 62 is frozenand the starting point 63 is signaled. Then the relative intensity 66 isintegrated and the time duration 76 along with the maximum peak 72 istracked until the relative intensity 66 goes below the trip point level74. This will signal the ending point 78 at which time the thresholdreference 60 will be released to be readied for the next flash interval80.

The specific equations below are preferably used and are optionallypreformed by a microprocessor are as follows:

Used for establishing the threshold level.

-   Where α=running average interval-    n=discrete sample number-    NT=noise threshold

$T_{i} = {{{\frac{1}{\alpha}{\sum\limits_{n = {i + 1}}^{\alpha + i}\sqrt{X_{n}^{2}}}} + {NT}}❘_{i = 0}^{\infty}}$Used for retrieving the sample intensity value.

-   Where α=running average interval-    n=discrete sample number

${SI}_{i} = {{\frac{1}{\alpha}{\sum\limits_{n = {i + 1}}^{\alpha + i}\sqrt{X_{n}^{2}}}}❘_{i = 0}^{\infty}}$Used to establish the beginning point of the flash interval. At thispoint in time the threshold level would be frozen until the sampleintensity value gets below the threshold level.

B = SI_(i) > T_(i)❘_(i = 0)^(∞)Used to establish the ending point of the flash interval.

E = SI_(i) < T_(frozen)❘_(i = 0)^(∞)Used to establish the total integrated intensity value.

$I = {{{\sum\limits_{B}^{E}{SI}_{i}} - T_{frozen}}❘_{i = 0}^{\infty}}$Used to establish the total time captured for the flash interval

$C = {{\sum\limits_{B}^{E}i}❘_{i = 0}^{\infty}}$Used to establish the peak intensity value.

P = SI_(i)max ❘_(i = 0)^(∞)

It will be appreciated that the examples provided in the instantspecification and claims are set forth by way of illustration and do notdepart from the spirit and scope of the instant invention. It is to beunderstood that the instant invention is by no means limited to theparticular embodiments herein disclosed but is much broader, it alsocomprises any modifications or equivalents within the scope of theclaims.

1. An apparatus for detecting the presence of flame in the exhaust pathof a gas turbine engine comprising: an optical viewing port mounted to agas turbine engine exhaust section to collect radiant energy present inthe exhaust path; a sensor element comprising at least one spectrometerhaving a diffraction grating for refracting the radiant energy intodifferent wavelengths and further having a detector array comprising aplurality of detectors, each detector sensitive to specific wavelengthsof the refracted radiant energy produced from flame transmitted fromsaid optical viewing port, wherein said sensor element emits anelectrical signal when radiant energy is present; and, a microprocessor,for receiving and interpreting the electrical signal in comparison topredefined parameters, connected to said sensor element and activatedwhen flame has been detected in the exhaust path of the gas turbinecausing the electrical signal, wherein the microprocessor produces anoutput relative to the electrical signal.
 2. The apparatus for detectingthe presence of flame in the exhaust path of a gas turbine engine ofclaim 1 further comprising: a fiber optic cable assembly mounted toreceive the radiant energy from the optical viewing port and to transmitthe radiant energy to the sensor element.
 3. The apparatus for detectingthe presence of flame in the exhaust path of a gas turbine engine ofclaim 1 further comprising: a computer to receive the microprocessoroutput and make a determination of the state of the fuel nozzle clog. 4.The apparatus for detecting the presence of flame in the exhaust path ofa gas turbine engine of claim 1 further comprising: a storage devicecapable of saving said electrical signal from said sensor element forlater analysis.
 5. The apparatus for detecting the presence of flame inthe exhaust path of a gas turbine engine of claim 1 further comprising:a fiber optic cable assembly mounted to receive the radiant energy fromsaid optical viewing port; a collection optics to receive the radiantenergy from said fiber optic cable and efficiently couple the radiantenergy to said sensor element.
 6. A method of determining the state ofthe fuel nozzle of a gas turbine comprising the steps of: receivingradiant energy from the exhaust path of a gas turbine; transferring theradiant energy to at least one sensor capable of detecting radiantenergy; determining an average of a baseline intensity of a normalbackground intensity of the radiant energy of a gas turbine known to beoperating efficiently with clean fuel nozzles; producing an electricalsignal from the at least one sensor relative to the radiant energy;comparing the electrical signal to the average of the baselineintensity; indicating when radiant energy having an intensity greaterthan the baseline intensity has been received from the exhaust path. 7.The method of determining the state of the fuel nozzle of a gas turbineof claim 6, further comprising the step of amplifying the radiant energyfrom the exhaust path of the gas turbine.
 8. The method of determiningthe state of the fuel nozzle of a gas turbine of claim 6, furthercomprising the step of filtering the radiant energy to a wavelength ofabout 200 to about 800 nm.
 9. A method of determining the state of thefuel nozzle of a gas turbine, comprising the steps of: receiving radiantenergy from the exhaust path of a gas turbine; transferring the radiantenergy to at least one sensor capable of detecting radiant energyproduced from a flame present in the exhaust; determining the average ofthe baseline intensity of the normal background intensity of the radiantenergy of a gas turbine known to be operating efficiently with cleanfuel nozzles; producing a signal from the at least one sensors when theradiant energy in the 200 nm to 800 nm range has been received from theexhaust path; comparing the signal of the sensor to the average of theknown baseline intensity; and signaling the presence of flame when thesignal produced has a relative intensity greater than that of theaverage baseline intensity.
 10. The method of determining the state ofthe fuel nozzle of a gas turbine of claim 9, further comprising thesteps of storing the baseline intensity and signal produced from asensor that indicated the presence of a flame in the exhaust.
 11. Themethod of determining the state of the fuel nozzle of a gas turbine ofclaim 9, further comprising the steps of: measuring the duration of timethat the relative intensity of the signal produced is greater than thebaseline intensity; and indicating to the operator of the gas turbine ifthe duration of time exceeds 30 ms.
 12. The method of determining thestate of the fuel nozzle of a gas turbine of claim 9, further comprisingthe steps of: measuring the intensity of the signal produced from thesensor; and, indicating to the operator of the gas turbine if the sensoroutput reaches a level greater than the average relative intensity ofthe baseline intensity by a predetermined amount based on the level ofturbine activity.
 13. A method of detecting the presence of flame in theexhaust of a turbine engine, comprising the steps of: gathering a lightenergy by a view port attached to the exhaust plenum of a turbineengine; transmitting said light energy by a fiber optic cable into aspectrometer through a fixed aperture; striking light energy against acollimating mirror in the spectrometer; directing said light energy fromthe collimating mirror at a diffraction grating; refracting the lightenergy into wavelengths by the grating; directing the refracted lighttoward a focusing mirror; reflecting the refracted light to strike ontoa focusing mirror; focusing the refracted light onto a detector arraycomprising a plurality of detectors; concentrating the refracted lightin front of the detector array with a lens onto an individual detector;responding to an individual wavelength of light that strikes a detectorelement (pixel) with an electrical signal; feeding said signal into amicroprocessor; interpreting a signal strength and information relativeto the intensity of the individual wavelengths of light as received bysaid detector array, and providing information to an end user of the gasturbine.
 14. The method of claim 13, further comprising the step oflimiting the effects of second and third order wavelength harmonicsusing an order sorting filter.
 15. The method of claim 13, furthercomprising the step of determining the spectral nature of the flamecondition being monitored.
 16. A method of determining the presence offlame in the exhaust of a gas turbine, comprising the steps of:collecting spectral energy from the exhaust portion of a gas turbine;transmitting said spectral energy to a sensor; producing an electricalsignal corresponding to the intensity and presence of a flame in theexhaust; storing the electrical signal in a storage device; providing acomputer processor to evaluate the electrical signal; and performingwith the computer processor operations, further comprising the steps of:establishing a threshold level$T_{i} = {{{\frac{1}{\alpha}{\sum\limits_{n = {i + 1}}^{\alpha + i}\sqrt{X_{n}^{2}}}} + {NT}}❘_{i = 0}^{\infty}}$ wherein α=running average interval, n=discrete sample  number, NT=noisethreshold; determining a sample intensity value${SI}_{i} = {{\frac{1}{\alpha}{\sum\limits_{n = {i + 1}}^{\alpha + i}\sqrt{X_{n}^{2}}}}❘_{i = 0}^{\infty}}$ wherein α=running average interval, n=discrete sample number; freezingthe threshold level until the sample intensity value gets below thethreshold level; establishing an ending point of the flash intervalB = SI_(i) > T_(i)❘_(i = 0)^(∞); establishing a total integratedintensity value E = SI_(i) < T_(frozen)❘_(i = 0)^(∞); establishing atotal time captured for the flash interval${I = {{{{\sum\limits_{B}^{E}{SI}_{i}} - T_{frozen}}❘_{i = 0}^{\infty}C} = {{\sum\limits_{B}^{E}i}❘_{i = 0}^{\infty}}}};{and}$establishing a peak intensity value P = SI_(i)max ❘_(i = 0)^(∞); whereinthe results of operations T₁, SI₁, B, E, I, C and P produced are storedin a memory device.
 17. The method of determining presence of flame inthe exhaust of a gas turbine of claim 16, further comprising the stepsof: comparing the stored results of operations T₁, SI₁, B, E, I, C andP; and determining that a condition requiring maintenance of the nozzlesexists.
 18. The method of determining presence of flame in the exhaustof a gas turbine of claim 17, further comprising the step of indicatingthat a condition requiring maintenance of the turbine exists.